This invention relates to a vehicle closure object detection circuit which utilizes a few low cost simple circuit elements, thus reducing the cost of the circuit. On the other hand, the circuit adapts to the individual system dynamics, and is thus quite dependable.
Vehicle closures are typically powered by a motor, at the control of an operator closure request switch. Thus, an operator will actuate a switch and the closure will move toward a closed position. Such closures include cab windows, moon roofs, sun roofs, etc.
There may sometimes be an obstruction in the closure path. As an example, a vehicle passenger could have an arm extending outwardly of a window. Known vehicle closure controls monitor a system characteristic, such as motor torque, speed, current, etc. If the monitored characteristic differs from an expected value, then a decision may be made by the control that an object is in the path of the closure element.
One problem with these circuits is that to store or calculate an expected value typically requires a complex control circuit. Often, microprocessor based controls are utilized. It would be desirable to achieve a circuit which provides a good prediction of an obstruction in the path of the closure with a relatively low cost.
Further, even these complex controls have had some difficulty in adapting to the individual characteristics of the particular system. Every component in the closure system has manufacturing tolerances. Each tolerance has the potential of moving the total response further the expected values. The prior art has not proposed a low cost, yet adaptable control circuit.
In a disclosed embodiment of this invention, a simple and low cost control circuit is designed which relies upon one simple assumption. The simple assumption is that the monitored characteristic will not change significantly, at least after an initial start-up period, unless an object is encountered. Thus, in a disclosed embodiment, a monitored characteristic is passed to a circuit element which delays the monitored characteristic from being considered. A difference between the delayed value, and a present value is then taken. This difference is compared to a threshold at a comparator. If the difference exceeds the threshold, then an indication is made that an object has been encountered.
Since the xe2x80x9cexpected valuexe2x80x9d is not predetermined but instead is an actual system characteristic, the circuit accounts for past tolerances and the individual system response.
The present invention achieves the above goals with a very simple circuit which includes a few simple circuit elements. In particular, a characteristic being monitored is delivered to two low pass filters. A first low pass filter removes high frequency components. The second low pass filter has a cutoff frequency much lower than a response expected when the system loads against an object. The second filter output is slow to respond to changes. Thus, the output of the second filter could be said to be the xe2x80x9cpastxe2x80x9d state of the system, whereas the output of the first filter is a present state. A difference of the two filter outputs is taken by a summing amplifier. That difference is passed to a comparator along with a threshold. If the difference exceeds the threshold then an indication is made that an object has been encountered. Essentially, this invention relies upon the assumption that the characteristic should not change significantly over the time of window travel. Thus, if the difference does exceed the threshold, an assumption is made that an object has been detected.
In further features of this invention, the threshold utilized at the comparator can decrease after a short start-up value. Typically, higher differences can be expected at start-up, and thus, the threshold will typically move to lower values after a short start-up period. Alternatively, an AND element can be incorporated into the circuit downstream of the comparator. The AND element will require not only an indication from the comparator that an object has been encountered, but further, an enabling signal is required. The enabling signal may be stopped during a start-up time transient. In this way, an indication of an obstruction during a short start-up transient will not be considered. The enabling signal can also be stopped at an end of travel position for the closure. In this way, the change in the characteristic when the closure hits the frame will not be identified as an obstruction.
The output from the first filter may also be passed to a second comparator, and compared to a second threshold. This can be utilized to determine an obstruction should the output of the second filter merely exceed a predetermined threshold. Typically, this second threshold will be higher than the first threshold. Thus, should there be an immediate spike in the monitored characteristic, the second threshold should be crossed and an indication of an obstruction will be quickly made.
These and other features of the present invention would be best understood from the following specification and drawings, the following of which is a brief description.